As shown in FIG. 1, a stepless expandable rod 10 of the prior art is composed of an outer tube frame 11, an outer tube wall piece 13, an inner tube 16, a connection rod 17, and a retaining member 18. The outer tube frame 11 has an inverted U-shaped cross section and an open face which is provided respectively in two sides thereof with a curved insertion edge 12. The outer tube wall piece 13 is provided along the direction of a longitudinal axis thereof with a plurality of round holes 14 and is further provided respectively in two side edges thereof with an insertion slot 15, which is engaged with the insertion edge 12 of the outer tube frame 11. The inner tube 16 is disposed in an outer tube formed of the outer tube frame 11 and the outer tube wall piece 13. The connection rod 17 is received in the inner tube 16. The retaining member 18 is disposed at the bottom end of the inner tube 16 and is connected with the bottom end of the connection rod 17. When the connection rod 17 is exerted on by an external force, the retaining projection 19 is actuated to move outward to engage the round holes 14 so as to retain the inner tube 16 in such a manner that the inner tube 16 is expanded for a predetermined length.
Such a prior art expandable rod 10 as described above is defective in design in that the outer tube frame 11 and the outer tube wall piece 13 must be made separately by extrusion, and that the outer tube wall piece 13 is then provided with the round holes 14 by punching, and further that the outer tube frame 11 and the outer tube wall piece 13 are fastened together by punching. It is therefore readily apparent that the prior art expandable rod 10 is not cost-effective.